Process for oxidizing olefins to aldehydes and ketones



United States Patent Office Patented Got. 8, 1963 The present invention relates to a process for oxidizing olefins to aldehy-des, ketones and acids.

It has already been proposed to oxidize ethylene catalytically by means of an argenti-ferous catalyst to ethylene oxide, or by means of an oxidation catalyst other than a silver-containing catalyst at a raised temperature to obtain mixtures of formaldehyde, acetaldehyde, formic acid, acetic acid and other products. These processes,

however, do not produce acetaldehyde or acetic acid in a yield interesting from an economical point of view. Our experiments have revealed that the oxidation carried out under such conditions in the presence of a noble metal catalyst likewise involves small yields of acetaldehyde, and the relative proportion of formaldehyde obtained generally preponderates.

It is also known that compounds of palladium, platinum, silver or copper form complex compounds with ethylene. Furthermore, the formation of acetaldehyde was observed in decomposing a potassium-platinumpomplex compound. Other unsaturated compounds may favor the complex formation. In this case stoichiometric reactions are concerned yielding the noble metalas such.

It has also been described to reduce palladous chloride by means of ethylene in the presence of water to palladium metal. In this reduction the formation of acetaldehyde was observed.

Still further, it has been described that palladous chloride dissolved in water can be reduced rapidly and completely to palladium by means of propylene, even if propylene is admixed with nitrogen or air. It has also been described to reduce palladous chloride by means of isobutylene under the same conditions. It is, however, known that carbon dioxide is not evolved either in this latter reduction or in those reductions which are carried out in the presence of ethylene or propylene as a reducing agent.

In application Serial No. 747,115, filed July 8, 1958, a process is described according to which carbonyl compounds can be obtained from the corresponding olefins in a good yield and, if desired, in a continuous manner, by contacting said olefins with gaseous oxygen, water which is present in the vaporous form, and a'solid catalyst which contains a compound of the mobile metals belonging to group VIII of the periodic table as catalytic substance and a redox system.

In application Ser. No. 760,539, filed September 12, 1958, now Patent No. 3,057,915, in which one of the present inventors is a co-inventor, it is described that the yield of acids which correspond to the aldehydes can be considerably increased without the aldehyde yield being reduced when an olefin is contacted with gaseous oxygen in the presence of water vapor and a solid acid to neutral catalyst containing as carrier a compound of a noble metal of group VIII of the periodic system and a redox system containing one or more compounds of one or more metals having an atomic number in the range from 25 to 27, i.e. iron, manganese, and/ or cobalt.

It has been mentioned in the aforesaid applications that the reactants may be diluted by gases inert towards the reaction, for example by nitrogen, carbon dioxide,

methane, ethane, propane, butane, isobutane and other saturated aliphatic compotmds and, furthermore, by other compounds, such as :cyclohexane, benzene or toluene.

Moreover, it has been disclosed in application Ser. No. 763,691, filed September 26, 1958, and now abandoned, that the olefins may be diluted by carbon monoxide and/ or hydrogen and that the course of the reaction is not affected by the presence of these gases.

Finally, it has been disclosed in application Ser. No. 768,624, filed October 21, 1958, that especially good results are obtained if the molar ratio between copper and halogen, and more especially between copper and chlorine, is kept within a range between 1 ml and 1 to 2, preferably between '1 to 1.4 and l to 1.8.

In the aforesaid applications the term carbonyl compounds is used in its broad sense, i.e. it covers not only aldehydes and ketones but also carboxylic acids, such as acetic acid.

Since the aforesaid process is carried out in the gaseous phase at a solid bed catalyst, care must be taken that the heat evolved during the process (the heat effect is high; about kcal are set free per mol of aldehyde) is dissipated to the exterior. These difliculties become more and more pronounced with an increasing space/ time/yield. In order to prevent too strong an increase in the reaction temperature, which may be, for example, within the range of C. and 170 C., but may be lower or higher, it may prove advantageous to carry out the reaction in a tube furnace. In order to produce a suflicient heat transition, the individual contact tubes should have a diameter not exceeding mm. and they should be made of a material which has a suflicient thermal conductivity and is not corroded by the catalyst. Since the catalysts used contain noble metal compounds, for example palladium compounds, it is less suitable to use the usual metals and alloys as tube material, since there is the risk that these less noble metals, in the presence of water and at the indicated temperatures, precipitate the noble metal salt used in the catalyst, and that they themselves are converted into salt form. Plastic material is likewise not very suitable because of its poor thermal conductivity, and the same applies approximately to tubes lined with ceramic material. In addition thereto, plastics have often relatively low softening points.

We have now found that it is especially advantageous to use a reactor which, on principle, comprises several stages, each of which has a contact zone of solid catalyst and a cooling zone.

The reaction mixture having preferably a temperature between C. to C. or even higher, elg. C., and consisting of olefin or olefin-containing gas, oxygen or air and, suitably, water vapor and hydrogen halide, or substances splitting off hydrogen halide under (the reaction conditions, for example those indicated above, flows through a catalyst layer in which it is converted to the corresponding aldehyde, possibly to the ketone and the corresponding acid, or to one of these products. The rate of conversion should not exceed a degree where the reacted gas mixture escaping from the catalyst is heated to an excessively high temperature. -In the cooling zone water is then added to the hot gas mixture in an amount, such that by heating and evaporating the water added, the said gas mixture is again cooled to the catalyst inlet temperature of about 100 C., or even below that temperature. The apparatus must be so designed that liquid water is prevented from contacting the following solid bed catalyst layer, and that unevaporated water can be withdrawn, if desired. If the reaction is carried out under pressure and if it is desired to use a gas heated to a higher temperature, or if it is not intended to cool the reacted gas to 100 C., then water kept under pressure and heated to a higher temperature may be introduced. Contrary thereto, it

is desired to operate at a temperature lower than 100 C., it is necessary to use water which is kept under a correspondingly reduced pressure. The hydrogen halide or hydrogen halide donor which is preferably supplied during the reaction to the individual catalyst layers in order to avoid a decrease of the yields may be introduced, depend ing on its composition, at the head of the reactor, or in admixture with water into the cooling zone. If it is intended to produce aldehydes or ketones and acid, as is the case for example in the presence of salts of the elements 'having an atomic number of 25 to 27, i.e. manganese, iron or cobalt, and preferably of copper, as it is described in application Ser. No. 760,539, now Patent No. 3,057,915, aqueous solutions of the corresponding acids and/ or aldehydes or ketones may be substituted for water and introduced into the cooling zones.

According to the present invention there may be used as redox systems, for example, those which contain compounds of metals which under the reaction conditions employed may appear in various oxidation stages, for example compounds of copper, mercury, cerium, thallium, tin, lead, titanium, vanadium, antimony, chromium, molybdenum, uranium, nickel, or osmium, the latter preferably in admixture with other redox systems, and also inorganic redox systems other than specified above, such as sulfite/sulfate, arsenite/arsenate or iodide/iodine systems and/or organic redox systems, for example azobenzene/ hydrazobenzene, or quinones or hydroquinones of the benzene, anthracene or phenanthrene series.

As compounds of the noble metals of group VIII of the periodic table there may be used in the process of the present invention, compounds of palladium, iridium, ruthenium, rhodium or platinum. Compounds of these metals are believed to be capable of forming addition compounds or complex compounds with ethylene. If desired the oxygen may be used in admixture with an inert gas. The reaction may likewise be carried out in the presence of a noble metal.

The oxygen may be employed, for example, in the form of air, which is the cheapest oxidizing agent or in the form of air enriched with oxygen. The use of air is, however, confined to certain limits, if the unreacted gases are circulated, inasmuch as nitrogen concentrates as ballast material. Instead of ethylene there may also be used a gas mixture containing ethylene and, for example, saturated hydrocarbons.

The reaction may be supported or carried out by addition of an active oxidizer, such as ozone, peroxide compounds, especially hydrogen peroxide or sodium peroxide, potassium peroxide, potassium persulfate, ammonium persulfate, alkali percarbonate, alkali perborate, peracetic acid, diacetyl peroxide, benzoyl peroxide, toluyl peroxide, oxygen compounds of nitrogen, such as nitrogen dioxide and nitrogen pentoxide or mixtures of nitrogen oxides containing the same, nitryl halides, such as nitryl chloride, free halogen, such as chlorine, bromine, or bromotrichloride, halogen-oxygen compounds, such as chlorine dioxide, hypochlorous acid, chloric acid, perchloric acid, bromic acid, iodic acid, periodic acid, or compounds of the higher valence stages of metals, such as manganese, cerium, chromium, selenium, lead, vanadium, silver, molybdenum, cbalt, or osmium, for instance potassium permanganate, sodium bichromate, lead tetraacetate, vanadium pentoxide, silver difluoride, selenium dioxide, cerium-(IV) sulfate, osmium tetroxide. The addition of an active oxidizer facilitates the reformation of the higher oxidation stage of the active catalyst component which is necessary for carrying out the reaction. These oxidizing agents may also be produced during the reaction. If desired, an oxidizing catalyst may be added.

In the present reaction it is often advantageous to add, prior to or preferably during the reaction, a compound yielding anions under the reaction conditions app-lied, for example an inorganic acid, preferably a mineral acid, such as sulfuric acid, nitric acid or a volatile acid, such as hydrochloric acid or hydrobromic acid, or a salt, such as ammonium chloride, ammonium bromide, zinc chloride, aluminum chloride, iron chloride, chromic chloride, titanium tetrachloride, sodium hydrosulfatc, a halogen or a halogen-oxygen compound, for example those mentioned above, or thionyl or sulfuryl chloride, or also an organic substance, preferably a saturated aliphatic halogen compound of low molecular weight, such as ethyl chloride, propyl chloride, butyl chloride, acetyl chloride, benzoyl chloride, propionyl chloride, phosgene. Such addition enables a possible decrease of anions to be counteracted and the lifetime of the catalyst to be prolonged.

In case that non-volatile compounds yielding anions are used as listed above, these substances are, of course, added to the catalyst before the reaction, while the volatile compounds can be added as Well before as during the re action.

The present process is carried out in the presence of a solid catalyst at relatively low temperatures. Suitable contact supports (carriers) are, for example, silica gel, kicselguhr, pumice, silicates, TiO A1 0 active carbon, such as charcoal, acid ion exchangers, such as Amberlite lRC 50, Dowex types 50, Permutites, phenol-aldehyde-resins which are substituted by sulfonic acid groups, polystyrene resins which are substituted by sulfonic acid groups and cross linked by divinyl-benzene etc., or mixtures of such carriers.

The present process can be carried out at atmospheric pressure, under a reduced pressure, e.g. 250 mm. of mercury or under raised pressure, that is, under a pressure of up to 100, preferably of up to 50 atmospheres gauge. The process may be carried out under pressure regard less of whether the temperatures used are above or below C.

It is, furthermore, of importance to carry out the present process in an acid to neutral medium. The preferred pH-values are within the range between 0.8 and 3; higher pH-values between, for example 0.8 and 5 or 2 and 6, or lower pI-I-values of, for example, 0.5 may also be used, although such pH-values generally do not involve a special advantage. In the present reaction the solution with which the solid catalyst is impregnated may be adjusted so as to have a pH within the limits indicated above.

If the present process is carried out in the absence of noble metals and in the presence of inorganic redox systerms, as disclosed in application Ser. No. 765,272, filed October 6, 1958, generally a temperature between 50 and 250 C. more suitably between 100 and 250 C. and preferably between 130 and 200 C., and pressures above atmospheric pressure and below 400 atmospheres (gauge), more suitably between 20 and 200 atmospheres (gauge pressure) and preferably between 80 and atmospheres (gauge pressure) are applied. Of course, the reaction may be carried out at lower or higher temperatures, for example above room temperature, or under a higher pressure, for example at 450 atmospheres. In this embodiment of the present invention operating at pH values between 1 and 5 is most preferred, though operating at higher or lower pH values, for example at pH 0, is likewise possible.

In the present process sometimes the presence of a salt, such as sodium chloride or potassium chloride like that of hydrochloric acid or of other alkali metal or alkaline earth metal halides, such as LiCl, CaCl MgCl or other salts, such as FeCl FeCl CuCl or ZnCl may prove advantageous. By the presence of these salts, for example the reactivity of CuCl, which may be formed in the course of the reaction, may be improved.

The reaction may be supported by increasing the ethylene and/or oxygen concentration in the reaction space. This can be achieved, for example, by increasing the pressure. The ethylene concentration at the surface of the catalyst may be considerably increased, for example by using higher concentrations of metal salts binding ethylene, for instance copper, iron, mercury or iridium compounds, especially halides, or the sulfates, the latter especially when mercury is concerned. The gases may be circulated, for example a gas containing a few percent of unreacted oxygen.

Due to the presence of oxidizing agents acetic acid may be formed in a small amount in addition to acetaldehyde. If desired, the oxidation of acetaldehyde to acetic acid which is known in the art, may be combined with the reaction described above in order to omit partially or totally the aldehyde stage, or acetaldehyde may be oxidized in a second stage to acetic acid, for instance in the presence of manganese compounds.

Under the conditions specified above under which ethylene yields acetaldehyde, propylene yields preponderantly acetone and propionaldehyde. aand B-butylene yield preponderantly methylethyl ketone, the ot-butylene yielding also butyraldehyde, and isobutyraldehyde can be obtained from isobutylene.

In the case where higher olefins are concerned, such as pentene and its homologs, cyclohexene or styrene, the reaction proceeds substantially in a manner analogous to that described and it can be carried out under the same conditions as set forth above. Due to the relatively mild reaction conditions there are almost exclusively obtained those oxidation products which had to be expected in view of their structure, without noteworthy isomerizations or molecule decompositions occurring.

Mixtures of olefins or gases containing olefins or other unsaturated compounds may be reacted in the same manner, provided they are capable of reacting under the reaction conditions, for example diolefins. The reaction of olefins containing 2 to 3 carbon atoms is, however, preferred. Under circumstances, the reaction conditions must be adapted to the compounds used and to their physical properties. The higher boiling points of the reaction products may also require a corresponding modification of the reaction conditions. Diacetyl may be obtained, for example, from butadiene.

The olefins may, however, not only be diluted by one or more of the aforementioned gases but likewise by carbon monoxide and/ or hydrogen, if desired in addition to the aforementioned gases. If such gas mixture contains CO, oxygen should be present at least in an amount as is necessary to convert the olefin to aldehyde and carbon monoxide to carbon dioxide.

It is believed that olefin-noble metal complex compounds are formed as intermediary products which then react with Water to yield carbonyl compounds. It is, however, known from the literature that carbon monoxide expels from these coordination compounds all olefins, including ethylene. For these reasons a mixture of olefins with carbon monoxide was expected to bring about none or only a very small conversion of the olefin to carbonyl compounds. It is, therefore, surprising that a mixture of carbon monoxide and olefin, if desired in admixture with one or more other gases inert towards the reaction, such as those mentioned above, practically yields the same amounts of carbonyl compounds as if no carbon monoxide were present. In this reaction the carbon monoxide is partially converted to carbon dioxide.

It is also known from the pertinent literature that hydrogen reacts in a manner very similar to that of carbon monoxide, and it is, therefore, just as well surprising that the olefin oxidation takes an absolutely smooth course in the presence of hydrogen. The major amount of hydrogen remains unaltered, whereas a small portion thereof reacts with formation of water and another small portion with hydrogenation of the olefins.

The carbonyl compounds can be obtained in the same manner without a reduction in conversion occurring by using a mixture of carbon monoxide and hydrogen with an olefin or a gas containing an olefin; in this case it is sometimes favorable for the conversion to work with the application of pressure.

The fact that neither hydrogen nor carbon monoxide affects the process of the invention is of special advantage since accordingly industrial gases, for example refined gases or gases obtained in cracking processes may be used as starting materials. All expensive gas separations can, therefore, be dispensed with, although a prepurification or concentration of the olefin may prove advantageous, so that a considerably cheaper crude material can be used. Carbon monoxide and/or hydrogen may appear in the gas mixture, for example in double the amount of the olefin, and yet the olefin oxidation is not substantially impaired. This statement is, however, not intended to indicate a limit.

[As stated above, the reactants may be diluted by gases inert towards the reaction, for example by nitrogen, carbon dioxide, methane, ethane, propane, butane, isobutane and other saturated aliphatic compounds, and furthermore by other compounds, such as cyclohexane, benzene or toluene.

For stoichiometric reasons the molar ratio of olefin bond to oxygen must be 2:1 in the complete oxidation of olefins to the corresponding aldehydes or ketones. To prevent explosions, it is, however, preferred to use an oxygen deficiency, for example in the range of 2.5 :1 to 4:1. Still further it is preferred to work outside the range of explosivity, for example With a content of oxygen of 8-20 percent or 8-14 percent under pressure, and to circulate unreacted gas which consists-a-fter separation of the reaction produotsswbstantially of non-con verted olefin, if desired in admixture with other inert gases, such as nitrogen, and/or with hydrogen and/or carbon monoxide and which may further-more contain some oxygen. To this gas oxygen and the olefin, for example ethylene, are added as they are consumed.

If it is intended to prepare an additional amount of acids which correspond to the aldehydes without the aldehyde yield being considerably reduced, the olefin may be contacted with gaseous oxygen in the presence of water vapor at a solid acid to neutral catalyst comprising a carrier, a compound of the above-mentioned noble metals of group VIII of the periodic system and a redox system containing one or more compounds of one or more metals having an atomic number in the range from 25 to 27, i.e. iron, manganese and/or cobalt and preferably one or more copper compounds. This efiiect is unexpected inasmuch as it was supposed that part of the aldehyde formed would be oxidized in the catalyst to the corresponding acid; it could not be foreseen, however, that an additional amount of acid would be formed. The compounds of iron, manganese or cobalt may be added to the catalyst suitable for this embodiment in the usual manner. It is possible, for example, to impregnate the catalyst with the soluble salts of these elements and to convert these salts by heating, preferably with air, to the firmly adhering oxides. There may also be used a mixture comprising the aforesaid compounds.

The simultaneous production of carboxylic acids and aldehydes at solid catalysts containing an iron, magnanese and/or cobalt salt, is preferably carried out in the presence of further redox systems, such as copper compounds.

The process of this invention is preferably carried out by contacting the olefin and oxygen or air simultaneously with the catalytic substances.

In a frequently useful technical variant of the process of this invention the desired reaction products, for example acetaldehyde and, if desired, acetic acid, are separated from the reaction gas, the residual gas which may still contain inert gases and/or hydrogen and/or carbon monoxide and may be free from oxygen, but may likewise contain'some oxygen, is reintroduced and an amount of olefin and oxygen corresponding to that consumed during the reaction is introduced into the reactor through one or more inlets, which may be arranged one above the other or one behind the other, or the olefin and/or the oxygen are added to the circulating gas. For example. the ethylene or ethylene-containing gas is admixed with the residual gas in an amount corresponding to that consumed. The resulting gas mixture containing, for example 90-95 percent of olefin -(for example ethylene) and 10-5 percent of oxygen, is then introduces into the reactor as well as an amount of oxygen corresponding to that consumed. For the sake of security the oxygen, if desired in admixture with insert gases, such as present in air, is preferably introduced through separate inlets, especially when no diluting gas is present and about stoichiometric amounts of the reactants are applied.

In order to obtain especially high space-time yields, it is also possible to introduce either olefin or oxygen, or olefin and oxygen into the reaction vessel, for example a reaction tower, at various places arranged one above the other or one behind the other. Preferably the inlets for each reactant are locally separated from the other inlets for the same reactant. It is likewise possible that the amount of oxygen introduced is measured so as to keep at all places of the reaction vessel below the lower limits of the explosive range.

In many cases the reaction proceeds likewise smoothly if the catalysts used contain only a small amount of compounds of the noble metals belonging to group VIII of the periodic table. In most cases it is suflicient to use a catalyst in which the ratio of the sum of the redox metals, especially the sum of copper and iron to the noble metal, especially palladium, is at least 15:1, preferably 25-500: 1. It is, however, preferred to use a catalyst containing copper salts, in which the ratio of copper to palladium is above 10: 1, for example above 15:1 and preferably 50:1 to 500:1, or even above these ranges. This method of operating is more economic in view of the fact that the expensive palladium salt need only be used in a minor amount; it can be used for converting ethylene and olefins other than ethylene, and may be combined as desired with variants hereinbefore or hereinafter described. This embodiment may also be carried out under elevated pressure.

In view of the fact that when using copper containing catalysts in the present reaction the conversion is de pendent inter alia on the molar ratio of copper to halogen, it has proved very favorable to keep the molar ratio of copper to halogen and more especially of copper to chlorine within the range between 1:1 and 1:2, prefera'bly between 1:1.4 and 1:18. It is, therefore, advisable to add the halogen during the reaction in very accurate dosages.

The above ratio of copper to halogen should be understood to include the amount of halogen added in the form of iron halide or other halides of cations which do not form neutral reacting salts with hydrohalic acids. The amount of halogen which is present in the form of a neutral salt, e.g. sodium chloride or potassium chloride, or is capable to be bound to form a neutral salt need not be considered. For example, if the catalyst contains 3 gram equivalents of alkali metal salts or alkaline earth metal salts of acids other than hydrohalic acids and 5 gram equivalents (mols) of chlorine ions added in the form of iron chloride, and one mol of copper anions added in the form of copper acetate, the copperzchlorine ratio is 1:2 according to the definition given above.

If halogen is present in a proportion smaller than corresponds to the ratio of 1:1, the conversion is reduced. In this case the optimum ratio can be easily readjusted, for example by addition of a hydrogen halide, such as hydrochloric acid. If halogen is supplied per se, the introduction of olefins is preferably interrupted for a short time since otherwise side-reactions may occur to a certain extent.

Instead of using halogens or hydrogen halides for regulating the copper:halogen ratio, there may also be employed compounds yielding halogen ions under the reaction conditions, such as halogen-oxygen compounds or organic substances, for example saturated aliphatic halogen compounds of low molecular weight, such as ethyl chloride.

If the catalyst contains more halogen than corresponds to the copperzhalogen ratio of 1:2, the reaction is retarded. The amount of halogen compound necessary to adjust the proposed optimum ratio can be readily calculated and controlled by periodic analyses. In order to immediately adjust the optimum copperzhalogen ratio in a fresh catalyst, part of the necessary cupric chloride may be replaced by cuprous chloride or copper acetate. This enables high conversions to be obtained from the beginning of the reaction.

The reaction of the present invention is favorably influenced by irradiation with rays rich in energy, preferably ultraviolet light. Such irradiation which may also comprise X-rays activates especially the oxygen, increases its oxidation activity, and promotes both the reaction with the olefin and a possible oxidative destruction of byproducts, for example oxalic acid. These measures increase the conversion, reduce the formation of by-products and considerably prolong the lifetime of the catalyst, the activity of which may subside after a prolonged time.

In practice it is advantageous to use a mercury quartz lamp as source of radiation arranged in the catalyst so that the light energy is fairly substantially utilized. If the reaction is carried out with an apparatus into which oxygen or an oxygen-containing gas is introduced separately from the olefin or olefin-containing gas or even a mixture of the said reactants, it is preferred to arrange the source of radiation in the vicinity of the oxygen inlet, so that that part which is rich in oxygen is especially well irradiated. The oxygen is thereby activated as long as it has a high partial pressure. Activation may also be brought about by adding a compound of a radio-active element to the catalyst solution.

The conversion and the space-time yield in the present reaction depend, for example, on the residence time in the apparatus and the composition of the catalyst, the temperature and the pressure used. The most suitable residence time can readily be determined by a simple test.

In the reaction condensates which separate from the reaction product, especially aqueous condensates, may also be recirculated to be reused as cooling agent, for example as such or after separation of lower boiling reaction products.

It is not necessary that the catalysts used are made of fine chemicals; they may likewise be produced from suitable metals of commercial purity. Metals, such as copper and iron, may be readily dissolved even by not-oxidizing acids, such as hydrochloric acid and acetic acid, if desired by addition of an oxidizing agent, especially if copper is used, or by passing through during the dissolving process a gaseous oxidizing medium, such as oxygen or air enriched with oxygen. The contaminations contained in commercially pure metals do not affect the reaction if the solutions obtained are worked up to the solid bed catalysts used in the process of the present invention. More especially the catalytic activity remains practically unaffected by small amounts of foreign metals which may appear in copper or iron of commercial purity. The anion forming agents contained in metals, such as sulfur, phosphorus, carbon, silicium etc., are converted upon being dissolved to either hydrogen compounds, for example H 8, which escape together with the reaction gases, or oxidized to acids of a higher valence stage, for example H 50 which do not afiect the reaction, or are converted partially into insoluble compounds, for example CuS, which appear only in minor amount and, if necessary, can readily be separated from the catalyst, for example by filtration, before the catalyst solution is applied to the carrier.

The solutions so obtained are then admixed with the noble metal compound which is added in substance or in the dissolved state, if desired diluted with water, and the 9 concentration of hydrogen ions is adjusted to the degree desired; the solutions so prepared may then be concentrated and are applied to a carrier, for instance those mentioned above.

Solvents suitable for dissolving the metals are chiefly hydrochloric acid and acetic acid in view of the fact that the presence of these acids proves especially advantageous in oxidizing olefins to aldehydes, ketones and acids. Acids other than those indicated above may, however, also be used, for example nitric acid. In this case it is preferred to remove the acid in excess in order to adjust the solution to the pH desired and to use the solution so treated for impregnating the carrier. If desired the salt of the metals may partially be converted into the corresponding chlorides and/ or acetates.

Palladium chloride or other noble metal chlorides need not be used; there may also be employed the metals themselves, e.g. metallic palladium, suitably in a finely divided and finely distributed state, which reacts, for example, with copper chloride, and is converted to palladium chloride or a compound other than palladium chloride.

For example, the catalyst may contain as anion chlorine ions or halogen ions other than chlorine, such as fluorine or bromine ions, nitrates or chlorateor perchlorate radicals, or mixtures of these anions, for example, with sulfate or acetate radicals. Sometimes it is especially advantageous to use a catalyst which contains perchlorate ions.

Although the catalysts have generally a good activity even after a prolonged time of reaction, especially when anions are added during the reaction, it may be advantageous to regenerate the catalyst from time to time. Some variants for such regeneration methods are described hereinafter.

It may be that the activity of the catalyst, especially when the catalyst is used for a very long period of time, is more or less reduced by the formation of a minor amount of by-products, or by foreign substances which may have been introduced. The by-products formed consist partially of organic compounds which are water-soluble at least to a certain degree, such as acetic acid, oxalic acid, higher aldehydes or ketones, or chlorinated organic compounds. Foreign substances possibly introduced into the catalyst may derive from, for example, contaminations of the gases, or the corrosion of parts of the apparatus, for example, iron parts or of the lining of the reactor.

The catalyst may be freed from these contaminations and regenerated in a simple manner by precipitating the cupric chloride as cuprous chloride and the noble metal compound as elementary metal. The precipitation may be eifected directly on the carrier or the catalytic compounds may be dissolved therefrom. Precipitation is preferably carried out with the exclusion of substantial amounts of oxygen by the action of carbon monoxide, hydrogen or one or more olefins, for example ethylene, propylene or the butylenes, or of any other olefin or a mixture of several of these precipitating agents. The mixture of cuprous chloride and noble metal or the solid catalyst in which these substances are precipitated are advantageously washed, e.g. with water. If a solution of the catalytic agents has been prepared it is mixed with water and an acid, suitably hydrogen chloride, if desired in the form of hydrochloric acid, and any, if desired after the addition of a salt of iron, manganese and/or cobalt or of another metal than those mentioned above, be reused in the impregnation in this state or, if desired, after oxidation with oxygen or an oxygen-containing gas, such as air. If the cuprous chloride and the noble metal are precipitated in the carrier, the washed carrier may be treated with a solution of a salt of one or more of the metals mentioned above, such as iron, manganese and/or cobalt and with an acid, such as hydrochloric acid. If desired, the catalyst may additionally be oxidized, e.g. by means of oxygen or chlorine, and then reused. If a separate oxidation is dispensed with and olefin and oxidation agent are allowed to act simultaneously upon the catalyst to be reused, oxidation is brought about in the following reaction by the oxygen contained in the reaction gas. catalyst has been reintroduced into the reactor, the amount of oxygen contained in the reaction gas may temporarily be increased, if desired. If in reducing the catalyst oxygen is not completely excluded, it is only necessary to use a somewhat larger amount of reducing agent.

This mode of execution is especially interesting if in addition to the noble metal the catalyst contains substantial amounts of copper salts, since these two rather expensive components of the catalystCuCl and noble metalprecipitate, while all other impurities or additions, for example iron salts, remain in the solution and are thus separated from the expensive noble metal and copper compound.

The noble metal is quantitatively precipitated as Well as CuCl, except for a minor amount thereof which is soluble in water. In reusing the catalyst it is, therefore, advisable to add the corresponding amount of fresh CuCl and/or CuCl-I-HCl. The further Well soluble and frequently cheap additions, such as iron salts, are suitable to be replenished.

The simplest manner of allowing CO and/or 'olefins and/ or hydrogen to act upon the catalyst is to introduce these substances upon the catalyst or into the solution prepared as described above. In most cases this may be done under normal conditions, but it may be advantage ous to use a higher temperature and/ or a raised pressure. More severe conditions are opportune, especially when hydrogen is used, which is the weakest reducing agent among the substances mentioned above. In using olefins as reducing agents the oxidizing activity of the catalyst may be used for a further formation of aldehydes, ketones and acids.

It is, furthermore, advisable prior to allowing the above gases to act upon the solution which is obtained by dissolving the active components from the carrier to entirely or partially neutralize or buffer the acid contained therein to a relatively low pH which is preferably in the range between 2 and 4. At too strong an acidity the reaction proceeds too slowly or is incomplete after the usual time of reduction. In addition thereto, CuCl is remarkably soluble in concentrated hydrochloric acid, which may involve losses of copper. It should be noted that a further amount of hydrochloric acid is formed during the reduction of the copper or noble metal chloride, and this amount of acid must possibly also be neutralized or buffered. Reduction at a pH higher than 4 is often regarded to be disadvantageous since hydroxides are likewise precipitated, though a regeneration by precipitating the hydroxides or basic salts of the metals used is likewise possible.

Neutralization or buffering may be made in the usual manner with alkaline reacting substances, such as sodium hydroxide solution, sodium carbonate, sodium acetate, chalk, lime, and similar compounds. The said reducing gases may be circulated for reasons of economy and, especially if carbon monoxide is used, may also be subjected to a C0 wash.

According to another method of regeneration of the solid bed catalyst, the olefin supply may be arrested for a short while and the catalyst may be treated simultaneously with oxygen or oxygen-containing gases and steam and an acid in vapor form or gas form, preferably hydrogen chloride or hydrogen bromide. A variant of such regeneration consists, for example, in passing oxygen or an oxygen-containing gas partially or completely and prior to contacting the catalyst through aqueous hydrochloric acid, preferably at a raised temperature. Accurately dosing the hydrochloric acid is especially simple, if a 20 percent hydrochloric acid is used.

The catalyst which prior to this treatment has possibly a metallic lustre turns agains brown and regains its initial After the regenerated but not yet oxidized 11 activity, possibly after an induction period of several hours.

The apparatus used in the prmess of this invention should be made of a material which has a suificient thermal conductivity and is not corroded by the catalyst. Since the catalysts used contain noble metal com-pounds, for example palladium compounds, it is less suitable to use the usual metals and alloys as construction material, since there is the risk that these less noble metals, in the presence of Water and at the indicated temperatures, precipitate the noble metal salt used in the catalyst, and that they themselves are converted into salt form.

In order to avoid corrosion in the apparatus used, it is often suitable to use an apparatus lined with titanium or titanium alloys containing at least 30 percent of titanium, or with tantalum. There may also be used glass vessels or enamelled or rubber-lined vessels. The reaction may also be carried out in brick-lined vessels or, under suitable reaction conditions, in vessels the insides of which are lined with plastic material, for example polyolefins, polytetrafiuorethylene or hardenable unsaturated polyesters, or phenol-, cresolor xylenol-formaldehyde resins. As brick lining there may be used, for example, ceramic material, carbon bricks impregnated with hardenable artificial resins and similar known materials.

The following example illustrates the invention but is not intended to limit it thereto.

Example A reactor comprising reaction stages is charged, per hour, with 100 mols of ethylene, 50 mols of oxygen and 50 mols of steam. Each reaction stage comprises a contact zone and a cooling zone. The contact zone contains 1.7 liters of a catalyst containing 22.6 grams of palladous chloride, 34.6 grams of cupric chloride, and 765 grams of silica gel. The gas mixture entering the reactor at the head has a temperature of 110 C. 1.7 mols of acetaldehyde are obtained per contact zone. The mixture of reaction gases leaving the contact zone has a temperature of 150 C.; it is mixed With 7.5 mols of water and cooled in the following cooling zone to 110 C. The gas mixture so cooled then enters into the following contact zone. Chlorine entrained is replaced in the cooling zones by continuous addition of hydrochloric acid.

We claim:

1. A process for the conversion of an olefinic hydrocarbon to a carbonyl compound selected from the group consisting of aldehydes and ketones by oxidation of an olefinic carbon atom of said olefinic hydrocarbon to a carbonyl group, which process consists essentially of contacting said olefinic hydrocarbon and oxygen, in a neutral to acid medium, with water vapor and a supported solid catalyst of (a) a salt of a noble metal selected from the group consisting of palladium, iridium, ruthenium, rhodium, and platinum, and (b) as a rcdox system, an inorganic salt of a metal showing several valence states under the reaction conditions applied, said contacting being effected by passing the reactants through a successive plurality of contact zones wherein the reactants are contacted with the catalyst to oxidize at least a portion of said olefinic hydrocarbon, and of cooling zones, alternating with said contact zones, wherein reaction products and unreacted reactants are contacted with water to absorb the exothermic heat of reaction developed in the preceding contact zone before passing to the next succeeding contact zone.

2. A process as in claim 1 wherein anions selected from the group consisting of chlorine anions and bromine anions are present in the catalyst, and are supplied to the catalyst during the reaction.

3. A process as in claim 1 wherein the reactants and catalyst are contacted in said contact zones at a temperature between 50 C. and C. at a pressure between about atmospheric pressure and 50 atmospheres gauge pressure.

4. A process as in claim 3 wherein said salt of a noble metal is palladium chloride, said salt of a metal showing several valence states is copper chloride, and wherein halogen anions selected from the group consisting of chloride anions and bromine anions are supplied to said catalyst during the reaction.

References Cited in the file of this patent UNITED STATES PATENTS 1,999,620 Van Peski et al Apr. 30, 1935 2,055,269 Van Peski et al. Sept. 22, 1936 2,333,216 Trieschmann et al. Nov. 2, 1943 2,451,485 Hearne et al. Oct. 19, 1948 2,486,842 Hearne et al. Nov. 1, 1949 2,690,457 Hackm-ann Sept. 28, 1954 FOREIGN PATENTS 664,879 Germany Apr. 1, 1930 713,791 Germany Nov. 14, 1941 891,209 France Mar. 1, 1944 575,879 Great Britain Feb. 25, 1946 OTHER REFERENCES Phillips: Amer. Chem. Journal, vol. 16 (1894), p. 267. Chatt: Chemical Abstracts, vol. 48 (1954), pp. 5067- 5068. 

1. A PROCESS FOR THE CONVERSION OF AN OLEFINIC HYDROCARBON TO A CARBONYL COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALDEHYDES AND KETONES BY OXIDATION OF AN OLEFINIC CARBON ATOM OF SAID OLEFINIC HYDROCARBON TO A CARBONYL GROUP, WHICH PROCESS CONSISTS ESSENTIALLY OF CONTACTING SAID OLEFINIC HYDROCARBON AND OXYGEN, IN A NEUTRAL TO ACID MEDIUM, WITH WATER VAPOR AND A SUPPORTED SOLID CATALYST OF (A) A SALT OF A NOBLE METAL SELECTED FROM THE GROUP CONSISTING OF PALLADIUM, IRIDIUM, RUTHENIUM, RHODIUM, AND PLATINUM, AND (B) AS A REDOX SYSTEM, AN INORGANIC SALT OF A METAL SHOWING SEVERAL VALENCE STATES UNDER THE REACTION CONDITIONS APPLIED, SAID CONTACTING BEING EFFECTED BY PASSING THE REACTANTS THROUGH A SUCCESSIVE PLURALITY OF CONTACT ZONES WHEREIN THE REACTANTS ARE CONTACTED WITH THE CATALYST TO OXIDIZE AT LEAST A PORTION OF SAID OLEFINIC HYDROCARBON, AND OF COOLING ZONES, ALTERNATING WITH SAID CONTACT ZONES, WHEREIN REACTION PRODUCTS AND UNREATED REACTANTS ARE CONTACTED WITH WATER TO ABSORB THE EXOTHERMIC HEAT OF REACTION DEVELOPED IN THE PRECEDING CONTACT ZONE BEFORE PASSING TO THE NEXT SUCCEEDING CONTACT ZONE. 